On July 28th, 2004, Sunday released her first single in Japan, "Lira no Kataomoi". Her second single, "UsotsukiBOY", was produced by m-flo and released on April 20, 2005. In that same month, the group Chun Sang Ji Hee The Grace debuted in with the Korean single "Too Good" The group released their first single, "Boomerang" in Japan on January 25, 2006.

It is unknown whether or not Sunday will release any more songs as a soloist.